1. Field of the Invention
The present invention generally relates to an automatic resolution changing method and circuit for use in digital conversion of two-phase sinusoidal wave signals and, more particularly, to an automatic resolution changing method and circuit for use in digital conversion of two-phase sinusoidal wave signals, which provides high resolution during the low speed rotation of, for example, a resolver rotor or an encoder shaft, and which provides high followability during the high speed rotation thereof.
2. Description of the Related Art
Hitherto, conventional methods have been performed in conventional digital conversion circuits, as illustrated in FIG. 3, for digital conversion of, for instance, two-phase sinusoidal wave signals. That is, in FIG. 3, reference numeral 1 designates a first multiplying D/A converter for multiplying an output of a COS ROM 2, to which an angular output (xcfx86) of a known resolver (not shown) is fed back and inputted, by a sinusoidal component sin xcex8xc2x7sin xcfx89t of a resolver signal and for outputting a result of the multiplication, that is, sin xcex8xc2x7cos xcfx86xc2x7sin xcfx89t as a first converter output. Incidentally, xe2x80x9csin xcfx89txe2x80x9d denotes an excitation signal for the resolver.
Similarly, a second multiplying D/A converter 3 is operative to multiply an output of a SIN ROM 4, to which an angular output (xcfx86) of the resolver is fed back and inputted, by a cosinusoidal component cos xcex8xc2x7sin xcfx89t of a resolver signal and for outputting a result of the multiplication, that is, cos xcex8xc2x7sin xcfx86xc2x7sin xcfx89t as a second converter output.
A phase sensitive detection circuit 5 is connected to an output terminal of both the first multiplying D/A converter 1 and the second multiplying D/A converter 3. A signal representing a value obtained by subtracting the second converter output cos xcex8xc2x7sin xcfx86xc2x7sin xcfx89t of the second multiplying D/A converter 3 from the first converter output sin xcex8xc2x7cos xcfx86xc2x7sin xcfx89t of the first multiplying D/A converter 1 is inputted to the phase sensitive detection circuit 5, which then outputs a control residual xcex5. Incidentally, xcex5=sin xcex8xc2x7cos xcfx86xe2x88x92cos xcex8xc2x7sin xcfx86=sin(xcex8xe2x88x92xcfx86).
The control residual xcex5 is inputted to a compensator 6, from which an angular velocity dxcfx86/dt (=xcfx86dot) is then outputted. This compensator 6 is designed according to the characteristics of a counter 7 in the subsequent stage. For example, when the counter 7 has a first-order integral element, it is sufficient that a feedback control system is constituted in such a way as to have PI (Proportional+Integral) control elements, which include a first order lag filter, to thereby control the counter 7 stably with high accuracy at high speeds.
The angular velocity dxcfx86/dt (=xcfx86dot) is inputted to the counter 7, which is a plant, and then integrated therein and subsequently, outputted as a digital angular output xcfx86 (that is, an output counter value).
Incidentally, in the present specification, the angular velocity dxcfx86/dt and rotation angle are assumed to be expressed in electrical angles.
The conventional conversion circuit is configured as described above, and thus has the following drawbacks. That is, although the enhancement of resolution during the low speed rotation of, for example, a resolver rotor or of an encoder shaft, and the improvement of followability during the high speed rotation thereof are required of the aforementioned tracking system, which is a closed loop negative feedback circuit, for digital conversion of a resolver signal, the resolution with respect to the rotation angle is inversely proportional to the follow-up speed. Moreover, the range of the follow-up speed is uniquely determined according to the conversion performance of the circuit, so that the circuit is forced to be used within an allowable range of the follow-up speed. Thus, it is difficult to manage both the high resolution during the low speed rotation of, for example, a resolver rotor and the high followability during the high speed rotation thereof.
Further, the conventional conversion circuit has such a drawback not only in the case of applying this conventional conversion circuit to a resolver but the case of applying this conventional conversion circuit to an angular signal outputted by an encoder. That is, such a signal outputted from the encoder has no excitation component. The block configuration of the digital conversion circuit for digital conversion of an angular signal outputted from an encoder is obtained by removing the sin xcfx89t component of each of the signals and by omitting the phase sensitive detection circuit 5 therein. However, in such digital conversion circuit for digital conversion of angular signals outputted from an encoder, an angular velocity dxcfx86/dt (=xcfx86dot) outputted from the compensator 6 is integrated in the counter 7, and subsequently, the result of the integration is outputted as a digital angular output xcfx86. Therefore, the conversion circuit has a drawback similar to the aforementioned in the case of the circuit for digital conversion of a resolver signal.
The present invention was developed to eliminate the aforementioned drawbacks. Accordingly, an object of the present invention is to provide an automatic resolution changing method for use in digital conversion of two-phase sinusoidal wave signals, which provides high resolution during the low speed rotation of a resolver rotor or of an encoder shaft, and which provides high followability during the high speed rotation thereof.
To achieve the foregoing object, according to an aspect of the present invention, there is provided an automatic resolution changing method for use in a high-precision digital conversion of two-phase sinusoidal wave signals. This automatic resolution changing method comprises the steps of detecting a two-phase-sinusoidal-wave-like A-phase output and a two-phase-sinusoidal-wave-like B-phase output, which are outputted based on the rotation of a rotor with respect to a stator, integrating an angular velocity of the rotor on the basis of the control residual obtained from the two-phase sinusoidal wave signals in a counter, performing digital conversion of the rotation angle (xcex8) of the rotor with respect to the stator, and outputting a result of the digital conversion. Further, when the result of the digital conversion is outputted, in the case where the angular velocity is equal to or higher than a first percentage of a follow-up speed at a current resolution of the counter, the resolution of the counter is reduced, while in the case where the angular velocity is equal to or lower than a second percentage of the follow-up speed at the current resolution of the counter, the resolution of the counter is increased. Thus, the present invention can provide a method of performing digital conversion of two-phase sinusoidal wave signals.
Further, in the case of an embodiment of this automatic resolution changing method for use in a high-precision digital conversion of two-phase sinusoidal wave signals, when the resolution of the counter is reduced, the resolution thereof is reduced by 1 bit. Moreover, when the resolution of the counter is increased, the resolution thereof is increased by 1 bit. Thus, the present invention can provide a method of performing digital conversion of two-phase sinusoidal wave signals, which provides good followability.
Moreover, in the case of an embodiment of this automatic resolution changing method for use in a high-precision digital conversion of two-phase sinusoidal wave signals, the above first percentage is 87.5%, and the second percentage is 37.5%. Thus, the present invention can provide a method of performing digital conversion of two-phase sinusoidal wave signals, which provides high followability.
Furthermore, according to another aspect of the present invention, there is provided an automatic resolution changing circuit for use in digital conversion of two-phase sinusoidal wave signals. This automatic resolution changing circuit has a first converter for receiving a two-phase-sinusoidal-wave-like A-phase output, which is outputted based on the rotation of a rotor with respect to a stator, and for outputting a first converter output, a second converter for receiving a two-phase-sinusoidal-wave-like B-phase output, which is outputted based on the rotation of the rotor with respect to the stator, and for outputting a second converter output, a compensator for outputting an angular velocity of the rotor from the difference between the first converter output and the second converter output through a phase sensitive detection circuit, and a counter for integrating the angular velocity of the rotor, which is outputted from the compensator. This digital conversion circuit is adapted to perform digital conversion of a rotation angle of the rotor with respect to the stator and to output a result of the digital conversion. Further, this automatic resolution changing circuit for use in a high-precision digital conversion of two-phase sinusoidal wave signals, further comprises a changing circuit for reducing the resolution of the counter in a case where the angular velocity is equal to or higher than a first percentage of a follow-up speed at a current resolution of said counter for outputting the result of the digital conversion, and for increasing the resolution of the counter in the case where the angular velocity is equal to or lower than a second percentage of the follow-up speed at the current resolution of the counter for outputting the result of the digital conversion. Thus, the present invention can provide a circuit for performing high-precision digital conversion of two-phase sinusoidal wave signals, which provides high followability.